1. Field of the Invention
This invention relates to a system and process for disposal of dry fly ash, and more particularly, to a system and process for disposal of dry fly ash that effectively confines and damps fugitive dust during the collection, sorting, transporting, storage and treatment of fly ash at a landfill.
2. Description of the Related Art
Fly ash, or pulverised fuel ash as it is known in Europe, is one of the residual by-products generated during the high temperature combustion of coal in electric power generating plants, and more particularly, fly ash is the coal ash that exits a combustion chamber in the flue gas and is captured by air pollution control equipment, such as electrostatic precipitators, baghouses, and wet scrubbers at the power generating plant. The mineral constituents in coal, such as clay, quartz and shale, do not burn, but instead fuse and chemically recombine to form various crystalline and glassy phases of fly ash. Since the particles solidify while suspended in the flue gases, fly ash particles are generally spherical in shape. Fly ash particles typically comprise silicon dioxide (SiO2) (both amorphous and crystalline), aluminum oxide (Al2O3) and iron oxide (Fe2O3), along with small quantities of other oxides and alkalies. Fly ash is classified by ASTM as either Class F fly ash or Class C fly ash, with the main difference being the chemical properties of the fly ash resulting from the chemical content of the coal burned. Though a residual by-product, which many consider a waste, fly ash does not have any significant known environmental leaching problems, and with careful management and application, any such problems can be easily overcome.
Fly ash is a pozzolan, i.e., a siliceous or a siliceous and aluminous material that, in the presence of water (H2O) and lime (CaO), will combine to produce a cementious material. Lime often naturally exists in the fly ash or can be supplied by the addition of Portland cement or kiln dust. Fly ash is naturally of low permeability and in many applications is used with a binder, e.g., cement, lime, etc. For example, Class F fly ash typically contains less than 10% lime and requires an activating cementing agent to become a cementious material, whereas Class C fly ash typically contains more than 20% lime and is self-cementing without the addition of an activating cementing agent. The inherent low permeability and pozzolanic binding capacity make fly ash ideal for a wide range of environmental applications, such as ground remediation, landfill liners, road construction, etc.
Fly ash handling and disposal is an issue for the entire coal-burning industry. In the past, fly ash produced during coal combustion was simply entrained in the flue gases and allowed to freely disperse into the atmosphere. However, given the environmental and health concerns surrounding emissions of fly ash, numerous federal and state laws have been enacted to reduce such emissions. In response, coal-burning power plants have implemented various air pollution controls. Even with these air pollution controls, fugitive dust, i.e., solid airborne fly ash particles emitted from sources other than a stack or chimney, remains a problem. Based on the fine particulate nature and relatively low density of fly ash, it can easily be swept away by ordinary air currents, resulting in fugitive dust that ultimately settles in undesirable locations. As a result, the coal-burning industry is still addressing the ever present problem of fugitive dust.
Two (2) methods of handling and disposing fly ash have been predominately utilized in the coal-burning industry to damp and condition fly ash: the “slurry” method and the “dampening” method.
In the slurry method, the fly ash is mixed with water until the mixture has a water content of greater than 90% by weight. This mixture is transported from the power generating plant to a landfill where it stored as a slurry to minimize fugitive dust. The resulting impoundments are typically large and stable, but any breach of their dams is rapid and on a massive scale. For example, in December 2008, a dam breach at an impoundment for fly ash slurry at the Tennessee Valley Authority's Kingston Fossil Plant resulted in a major release of 5.4 million cubic yards of fly ash slurry, resulting in destruction of numerous homes and contaminating the Emory River, having an estimate cleanup cost of over $100 million dollars. A few weeks after the Kingston Fossil Plant incident, a smaller Tennessee Valley Authority impoundment breached, which contaminated the Widows Creek and the Tennessee River. Furthermore, given the large amounts of water needed for the slurry method, the transportation costs for hauling the fly ash slurry from the power generating plant to the landfill are greatly increased over transporting dry fly ash.
In the dampening method, the fly ash is mixed with sufficient amounts of water until the mixture has a water content of about 5% to 20% by weight. The dampening method adds just enough water to the fly ash to calm the fugitive dust. Similar to the slurry method, the costs for transporting the damped fly ash are greatly increased over the costs for transporting dry fly ash. Further, by damping the fly ash at the power generating plant, the damped fly ash may have begun to solidify in transport, prior to being dumped at the landfill.
It is therefore desirable to provide a system and process for disposal of dry fly ash that effectively confines and damps fugitive dust during the collection, sorting, transporting, storage and treatment of fly ash at a landfill.
It is still further desirable to provide a system and process for disposal of dry fly ash that virtually eliminates all fugitive dust when dry fly ash is dumped from a bulk transport truck at a landfill.
Other advantages and features will be apparent from the following summary, drawings and description and from the claims.